The present invention relates to a view angle control sheet, namely a sheet which passes light in some directions but not in other directions, and a method for producing it.
As sheets having a view angle control property, there have been known, for example, those described in Japanese Patent Publication No. Sho 47-43845, Japanese Patent Unexamined Publication No. Sho 63-309902, Japanese Patent Unexamined Publication No. Hei 6-82607 and the like.
Japanese Patent Publication No. Sho 47-43845 discloses a sheet having view angle control and obtained by laminating transparent discs and black discs alternately until a desired thickness is obtained and slicing the side surface of the laminated discs along the peripheries of the discs.
Japanese Patent Unexamined Publication 63-309902 discloses a view angle control film cured by ultra-violet rays from a specific direction to enable it to selectively scatter light of a specific irradiation angle. This patent document also teaches that light rays projected from two or more directions, i.e., rays projected with an angle component varying in two or more planes perpendicular to the film, can be selectively scattered, by curing the film with UV rays from two or more directions.
Japanese Patent Unexamined Publication No. Hei 6-82607 discloses a method for producing a view angle control film comprising folding a transparent polymer film with oriented polymer molecules using a blade or the like whose cutting edge is parallel to the direction of the molecular orientation and drawing the film in a direction perpendicular to the direction of the molecular orientation to produce cracks as stripes approximately parallel to the direction of the molecular orientation.
However, in the sheet of Japanese Patent Publication No. Sho 47-43845, since many transparent and black discs must be laminated until a desired thickness is obtained, the productivity is low and the obtained sheets are expensive. In addition, the sheet obtained by this method can control the view angle with respect to only one direction, i.e., it can control the view angle only with respect to light with an angle component varying in one plane perpendicular to the film and the laminated discs.
The film disclosed in Japanese Patent Unexamined Publication 63-309902 cannot completely shield light since it controls the transmission angle by reflection and scattering of angled rays. Further, it utilizes a special UV curing resin and its production requires a curing step, thereby resulting in expensive products. This method can provide sheets having view angle control property with respect to two or more directions. However, in order to provide such sheets, after producing a sheet having view angle control property in one direction, the steps of applying UV curing resin and exposure to UV rays must be repeated. This leads to extremely low productivity.
The method of Japanese Patent Unexamined Publication No. Hei 6-82607 is described as a method for overcoming the problems of the above prior art. However, this method requires films whose molecules are oriented. As such films, monoaxially stretched films are mentioned. However, in order to continuously produce the view angle control film with from a monoaxially stretching by this method, the monoaxially stretched film must have been stretched in the direction transverse to of the film. It is technically difficult to produce such a monoaxially stretched film and impossible to do so with sufficiently high productivity. In addition, in order to form cracks by this method, the film must be forced onto a blade with a quite large force while drawing the film. This step is likely to form many scratches on the film. Furthermore, the film obtained by this method has view angle control property for only one direction.
The present invention has been achieved to overcome the problems mentioned above and therefore an object of the present invention is to provide a view angle control sheet which can be easily produced at a low cost, exhibits excellent view angle control and can provide view angle control for as many directions as required. Another object of the present invention is to provide a method for producing such a view angle control sheet.